The man, 59, fell into a hole on the bank of the river where the bridge's counter-balance weights are located, allowing it to be raised and lowered, Roccasalva said.

The bridge had been lifted as workers did spring maintenance, said Roccasalva.

The worker suffered multiple injures and was taken to Northwestern Memorial Hospital at about noon in serious-to-critical condition as a precaution, said Roccasalva. The man's injuries were not considered life-threatening and his condition was stabilized, he said.